1. Field of the Invention
The present invention relates generally to a liquid developing device using a liquid developer and a concentrating agent, and more particularly to a storage unit for storing the liquid developer and the concentrating agent.
2. Description of the Related Art
With an accelerated development of copying machines and plotters in recent years, there has been an increased demand for a compact liquid developing device for used in these apparatus.
In a liquid developing device of the type concerned, the concentration of a liquid developer is gradually reduced with the consumption of a developer component (toner particles). A system is, therefore, provided for automatically detecting the toner concentration of the liquid developer to control the amount of a concentrating agent to be added to the liquid developer at need. The detection of the toner concentration relies upon an optical means or a measurement of the electric characteristics of the liquid developer. In this known system, when the concentrating agent is to be added, the concentrating agent is drawn from a storage tank which is provided separately from the liquid developer storage tank, and then it is introduced into a circulating path of the liquid developer. This means that the concentrating agent storage tank and a portion of the circulating path of the liquid developer are connected by a separate passage. In some cases, the separate passage includes an additional chamber. One such known developing device is disclosed by U.S. Pat. No. 4,222,497. The disclosed developing device is large in size because the liquid developer storage tank and the concentrating agent storage tank are disposed separately. Furthermore, due to this disposition of two independent storage tanks, these tanks are likely to be misplaced with each other when they are replaced.
One solution to the foregoing difficulties is proposed by U.S. Pat. No. 4,634,252 wherein a storage tank includes a first storage chamber for containing a liquid developer and a second storage chamber for containing a concentrating agent and operatively connected with the first storage chamber for directly replenishing the concentrating agent from the second chamber to the first chamber. With the storage tank thus constructed, the developing device is relatively small and free from the problem of misplacement of the development storage tank and the concentrating agent storage tank. However, since pipes which form part of respective circulating paths of the liquid developer and the concentrating agent extend close to the bottom of the storage tank, the liquid developer and the concentrating agent existing on or within the pipes are liable to fall onto the floor either directly or through the storage tank when the storage tank is removed, whereby the floor and operator's hands and clothes are smeared by the liquid developer and the concentrating agent. The storage chambers of the tank have flat bottom walls with the result that the amount of unused concentrating agent is relatively large.